Conventionally, techniques of controlling the concentration distribution or form of an air-fuel mixture in a combustion chamber have been known. For example, an engine according to Patent Document 1 performs first fuel injection in an intake or compression stroke to form a lean mixture in a combustion chamber, and then performs second fuel injection in the compression stroke to form a rich mixture, thereby reducing soot in the combustion chamber.
Patent Document 2 shows an outward opening valve type injector that injects fuel into the combustion chamber of an engine. In an outward opening valve type injector, the lift amount of a valve body is changed to change the effective cross-sectional area of a nozzle port injecting the fuel. Patent Document 3 shows a valve covered orifice (VCO) type injector. In a VCO type injector, a needle valve is set directly on a seat, to which a nozzle port is open, to close the nozzle port. In accordance with the lift amount of the needle valve, the size of the cavitation area on the inner peripheral surface of the nozzle port changes. As a result, the effective cross-sectional area of the nozzle port changes in accordance with the lift amount of the needle valve in a VCO-type injector, as in an outward opening valve type injector.
Patent Document 4 shows an engine including an outward opening valve type injector, which is located on the central axis of a cylinder and injects fuel in a cone shape. The fuel is injected into the cylinder at a terminal stage of a compression stroke to form a mixture layer in a combustion chamber and a gas layer (i.e., a gas layer containing fresh air) around the mixture layer. In the engine shown in Patent Document 4, at the combustion of an air-fuel mixture for forming the mixture layer, the surrounding gas layer functions as a heat insulating layer to reduce cooling loss.